Francis davis



s fi* 'I UFFICE.

FRANCIS DAvIs, CE KEENE, NEwHAursHIRE, AssICNoR To J. M. REED.

SCREW-JACK.

Specification of Letters `I1ate11t No. 10,902, dated May 9, 1854.

To all 107mm t may concern Be it known that I, FRANCIS DAvrs, of Keene, in the county of Cheshire and State of New Hampshire, have invented certain new and useful Improvements in Screw- Jacks; and I hereby declare the following to be a full, clear, and exact description of the same, reference being had to the annexed drawings, making part of this specification, in which- Figure l is a view of my screw jack, and Fig. 2 a section through the center of the saine.

In screw jacks as heretofore constructed a single screw has been made use of, and in order to give this screw the greatest possible amount of motion the head which re ceives the lever or bar by which the screw was moved was placed as near the top of jack as possible, and in consequence of this arrangement the operating lever or bar was brought immediately beneath the body to be raised and so near to it that its motion was much obstructed thereby.

To obviate this inconvenience and at the same time to produce a jack having capabilities not heretofore possessed by my instrument of the kind with which I am acquainted is the object of my present invention, which `consists in the use of a right and left screw, with the head or socketfor the operating lever between them, whereby the latter is removed to an equal distance from the top and bottom ends of the jack, andthe motion of the head `of the jack is double that of the ordinary screw jack for an equal motion of the operating lever and in an equal space of time, by which means a great saving of time and power is effected,

To enable others skilled in the art to make and use my improved jack I will proceed to describe its construction and operation.

My jack is made entirely of iron.

A is the head; B, the foot; C, the socket which receives the hand lever D for operating the jack. Attached to the socket C are the right and left screws E and F, which are adapted to corresponding females in the head and foot A, B. i

It is evident that as thelever D is turned to operate the screws E and F, the motion of the head of the jack will be double that which would be obtainable from the use-of a sinble screw with an equal amount of power applied. Thus the same amount of with an expenditure of but little more than` one half the power required for the operation of the ordinary jack, while the position of the operating lever is such that it is not obstructed either by the body above or the ground beneath.

I do not claim the use of a right and left screw, as this has been made use of before; neither do I claim constructing a screw-jack entirely of iron; but

W'hat I do claim as my invention and desire to secure by Letters Patent as a new tool or instrument for the purpose of raising heavy bodies is- Y The above described ack constructed and operating in the manner set forth.

FRANCIS DAvIs.

lVitnesses IVM. P. WHEELER, LUCIUs H. HAL-L. 

